Table of Contents
- 1. Engineering Foundation of Acoustic and Vibration Diagnosis
- 2. Low-Cost Field Diagnosis Methods
- 3. Extruder Fault Diagnosis
- 4. Injection Molding and Injection Stretch Blow Diagnosis
- 5. Extrusion Blow Molding Diagnosis
- 6. PET Bottle Blowing Machine Diagnosis
- 7. Recycling and Washing Line Diagnosis
- 8. Pelletizing Line Diagnosis
- 9. Fault Tree and Sound-to-Cause Lookup Table
- 10. Vibration Severity Standards (ISO 10816 / ISO 20816)
- 11. Spectral Identification of Six Typical Faults
- 12. Inspection Routines and Predictive Maintenance
- 13. Wanplas Group Machinery and Diagnosis Specification Tables
- 14. Application Industries
- 15. Requirement-to-Solution Recommendation
- 16. Wanplas Service and Support
- 17. Frequently Asked Questions
Engineering Foundation of Acoustic and Vibration Diagnosis
Abnormal sound and vibration are the earliest and most reliable physical signals that a plastic processing machine sends before a functional failure occurs. A machine that produces a steady, broadband, low-level mechanical hum is healthy; a machine that begins to whine, knock, rumble, or grind is broadcasting the location and nature of an internal fault through two independent physical channels: the acoustic pressure wave traveling through air and the structural vibration traveling through the machine frame, gearbox, and foundation. Learning to read these two channels is the single most cost-effective maintenance skill a plastic plant can build, because it lets you find a failing bearing, a misaligned coupling, or a scoring screw weeks before it stops production.
Wanplas, the main brand that aggregates the full plastic machinery value chain across its specialized factories, treats sound and vibration diagnosis as a shared discipline that applies to every product category it builds. Whether the equipment is a twin-screw compounding extruder, an extrusion blow molding machine, a PET bottle blower, an injection blow molder, a recycling washing line, a pipe extrusion line, or a sheet and board line, the underlying physics of fault signatures is the same. This article builds the diagnostic method from first principles so that a maintenance engineer can apply it across an entire plant.
Sound Pressure Level and the A-Weighting Scale
Sound is measured as sound pressure level in decibels, written as dB(A) when the A-weighting filter is applied. The A-weighting curve deliberately de-emphasizes very low and very high frequencies to approximate the sensitivity of the human ear, which is most sensitive around 1 kHz to 4 kHz. In a plastic plant, a healthy extruder gearbox typically emits 75 to 85 dB(A) at one meter, while a high-speed blow molder or a pelletizer cutting head can reach 90 dB(A) or more from airflow and material impact alone. The key is not the absolute level but the trend and, more importantly, the spectral character: a rising overall level coupled with a new tonal peak at a specific frequency is a far stronger diagnostic clue than a general increase in broadband noise.
Acoustic diagnosis works best for air-path faults such as hydraulic pump cavitation, valve squeal, compressed-air exhaust, and cutter impacts, because these generate pressure waves that radiate freely into the environment. Mechanical faults inside a closed gearbox or bearing housing are better captured as structural vibration, because the sound they radiate is heavily attenuated and masked by the surrounding machine noise.
Vibration Severity in Millimeters per Second RMS
Vibration is most usefully quantified as vibration velocity in millimeters per second, root-mean-square (mm/s RMS). Velocity is preferred over displacement or acceleration for general machine condition monitoring because it correlates well with the stress energy delivered to a bearing or structure across the typical fault frequency band. The international reference for evaluating this number is ISO 10816 and its updated successor ISO 20816, which sort measured overall vibration velocity into four evaluation zones:
- Zone A — good condition, vibration well below the limit for newly commissioned machines.
- Zone B — satisfactory, acceptable for unrestricted long-term operation.
- Zone C — unsatisfactory, can be operated for a limited period pending remediation.
- Zone D — unacceptable, risk of damage, stop and repair.
These zones are not universal constants; they depend on machine power, mounting (rigid foundation versus flexible isolation), and whether the measurement is on the bearing housing or the shaft. Section 10 of this article provides the reference tables by power class. The practical takeaway for a plant is simple: measure the same point, in the same direction, at the same machine speed, on a regular schedule, and watch which zone the trend line crosses.
Time Domain Versus Frequency Domain
Raw vibration as recorded by a sensor is a time-domain waveform: amplitude plotted against time. A time-domain trace is excellent for spotting impulsive events such as a broken gear tooth striking a mating tooth, or a loose component rattling once per revolution. However, most faults overlap in the time domain, and a single trace cannot easily separate a 1X imbalance from a 2X misalignment. The frequency domain solves this by applying a Fast Fourier Transform (FFT) that decomposes the waveform into its constituent frequencies, each shown as a peak at its frequency on the horizontal axis and its amplitude on the vertical axis.
FFT analysis requires attention to two parameters. The maximum frequency you can resolve is set by the sampling rate (the Nyquist limit is half the sampling rate), so capturing bearing defect frequencies that may sit at several kilohertz demands a sampling rate of at least several kilohertz. The frequency resolution, the spacing between adjacent FFT lines, is set by the length of the captured record; a longer capture window gives finer spacing, which matters when you need to separate 1X from 2X on a slow-running machine.
Characteristic Frequencies You Must Know
Every rotating or meshing component produces vibration at a predictable frequency derived from its geometry and speed. The most important are:
- 1X (rotational frequency) = shaft speed in revolutions per second = RPM / 60. Imbalance and many soft-footing problems appear at 1X.
- 2X (twice rotational frequency) — common with angular misalignment, certain coupling problems, and oil whirl.
- Gear Mesh Frequency (GMF) = number of teeth on the gear x shaft speed in Hz. A localized gear fault such as a chipped or pitted tooth modulates the GMF at 1X of the gear or pinion shaft, producing sidebands.
- Bearing defect frequencies — these are calculated from the bearing geometry (pitch diameter, ball diameter, number of rolling elements, contact angle) and the shaft speed:
- BPFO — Ball Pass Frequency Outer race
- BPFI — Ball Pass Frequency Inner race
- BSF — Ball Spin Frequency
- FTF — Fundamental Train Frequency (cage speed)
A fault on the outer race generates a peak at BPFO repeated once per shaft revolution, so it appears as BPFO surrounded by 1X sidebands. A fault on the inner race, which passes through the load zone, produces amplitude modulation at 1X as well, giving BPFO-like peaks but at BPFI with stronger sidebands. Recognizing which bearing frequency family is elevated tells you exactly which race or element is degrading.
Envelope Demodulation for Early Bearing Faults
The challenge with bearing faults is that the actual defect frequency peaks are often low in amplitude and buried beneath much larger vibration from gears, imbalance, and the machine structure. Envelope demodulation, also called high-frequency resonance technique, solves this. The method high-pass filters the raw acceleration signal to isolate the high-frequency structural resonance that the bearing defect excites each time a roller strikes the damaged spot. It then rectifies and demodulates (envelopes) that signal, removing the carrier resonance and leaving a low-frequency envelope that contains the true fault frequency (BPFO, BPFI, BSF, or FTF) with its 1X sidebands, now clearly visible above the noise floor.
Envelope demodulation is the single most valuable analytical tool for catching bearing degradation months before it becomes audible. A bearing that still sounds normal and still measures a healthy overall velocity can already show a clear BPFI peak in its envelope spectrum. When that peak appears, you have a scheduled window to plan a change-out rather than suffer an unplanned stoppage.
Low-Cost Field Diagnosis Methods
You do not need a laboratory or a six-figure analyzer to start diagnosing machines by sound and vibration. A disciplined program built on simple, low-cost instruments catches the large majority of developing faults, and it is the right starting point for any plant before investing in online monitoring. The goal of the low-cost tier is to establish a repeatable baseline, identify the obviously deteriorating machines, and route the urgent cases to deeper analysis.
The Mechanical Listening Rod (Stethoscope Rod)
A listening rod is a solid metal or acoustic-rod probe that transfers structural vibration from a contact point on the machine to the engineer’s ear. Press one end firmly against a bearing housing, gearbox wall, or motor frame, and place the other end to the ear (or a paired headset). The rod filters out airborne noise and reveals the internal character of the component: a healthy rolling bearing sounds like a smooth, even hiss; a pitted race sounds like gritty, irregular cracking; a dry or failing bearing sounds like a rhythmic clicking that repeats at the defect frequency. The listening rod is unbeatable for localizing which of several adjacent bearings is the culprit, because you move the contact point until the noise is loudest.
The Handheld Vibration Pen
A vibration pen (sometimes called a vibration meter) is a pocket instrument with a probe that reads overall vibration velocity in mm/s RMS, usually with a simple good/warning/danger indicator keyed to ISO 10816 zones. It gives no spectrum, but it is fast, cheap, and ideal for trending. A plant can assign one to each shift and require a weekly reading at a fixed set of measurement points. The value of the pen is the trend, not the single number: a bearing that climbs from 1.5 mm/s to 4.0 mm/s over three months is heading for trouble even though both readings sit in Zone B or C individually.
Smartphone Vibration Applications
Several general-purpose smartphone applications claim to measure vibration using the phone’s internal accelerometer. These have severe limitations: the built-in accelerometer is neither calibrated nor frequency-characterized for machinery diagnosis, the sampling rate is low, and no FFT or envelope analysis is available. At best, a phone app can confirm that a machine is violently shaking versus calm, and it can support a rough audio recording for later listening. It should never be used for acceptance testing, severity classification, or bearing life decisions. Treat it as a curiosity, not a tool.
Infrared Thermometry as an Auxiliary Channel
A portable infrared thermometer or thermal camera is not a vibration instrument, but temperature is a powerful companion signal. A bearing running hot relative to its neighbors, a gearbox sump climbing above its normal range, or a motor stator zone overheating all corroborate a vibration finding. Heat and vibration rise together as friction grows, so a machine that is both noisier and warmer is a high-confidence diagnosis. Keep in mind that surface temperature lags internal temperature, so a sudden temperature rise is already a developed fault; use trend, not absolute value.
Oil Ferrography and the Magnetic Plug
Wear does not only make noise; it makes particles. Most gearboxes and some hydraulic systems are fitted with a magnetic drain plug that catches ferromagnetic debris. A clean plug with a light fuzzy coating is normal; a plug heavy with metallic chips or a clump of fine “pepper” indicates progressing gear or bearing wear. Ferrography takes a lubricant sample and separates wear particles by size and type under magnification, distinguishing normal rubbing wear from abnormal cutting or fatigue wear. Combined with a whisper of new gear mesh noise, ferrography evidence of fatigue particles is a strong signal to open the gearbox before a tooth breaks.
Inspection Routes and Baseline Data
The foundation of every successful program is a written inspection route: a fixed list of machines, measurement points, directions (horizontal, vertical, axial), and frequencies, performed on a fixed schedule by trained staff using the same instrument. The single most important artifact is the baseline — the set of readings taken when each machine is new or freshly rebuilt and known healthy. Every future reading is compared against that baseline, not against a textbook number, because every machine has its own personality. Without a baseline, you are guessing; with one, you are trending.
Extruder Fault Diagnosis
The extruder is the heart of compounding, recycling pelletizing, sheet, pipe, and profile lines, and it concentrates several of the most diagnostic sound and vibration signatures in plastic machinery. The drive train (motor, coupling, gearbox, thrust bearing, screw) runs continuously under load, so faults announce themselves early if you listen.
Gearbox Gear Pitting and Broken Teeth
Symptom: A rhythmic knocking or heavy grating that grows with load, often accompanied by a fluctuating torque draw. Possible location: the reduction gearbox, most often the high-speed input stage or the final output pinion. Frequency signature: GMF with sidebands at the gear shaft speed (1X of the faulty gear); a broken tooth produces a high-amplitude impact at 1X of that shaft in the time domain. Verification: compare the gear mesh tone with the listening rod at the gearbox wall; confirm with ferrography and a magnetic plug check; an envelope or FFT analyzer shows the sideband pattern. Action: for pitting, schedule a gearbox inspection at the next planned stop and tighten lubrication; for a confirmed broken tooth, stop and replace the gear set, because a fragment can destroy the whole train.
Thrust Bearing Wear From Screw Axial Force
Symptom: A low rumble or growl from the rear of the gearbox that intensifies with head pressure and back pressure. The thrust bearing absorbs the enormous axial force generated by melt pressure pushing back on the screw. Possible location: the combined thrust and radial bearing at the screw output shaft. Frequency signature: elevated BPFO or BPFI of the thrust bearing in the envelope spectrum, often with strong 1X sidebands because the fault passes through the load zone. Verification: listen at the thrust housing with the rod; measure axial vibration; compare with melt pressure records — a rumble that scales with pressure is classic thrust wear. Action: reduce sustained peak back pressure where possible, verify thrust bearing preload, and plan a bearing change before axial play grows enough to damage the screw and barrel.
Screw and Barrel Scoring or Friction
Symptom: A continuous harsh grinding or scraping, sometimes a metallic scream, that tracks with screw speed and feed rate. Possible location: the screw flight rubbing the barrel wall, usually from worn screw coating, embedded hard contamination, or a bent screw. Frequency signature: broadband increase with no clean tone; in severe cases a tonal component near screw rotational frequency. Verification: correlate with rising motor load and melt temperature instability; a borescope inspection of the barrel and a screw runout check confirm contact. Action: stop feeding hard contamination, inspect and rebuild or recondition the screw, and measure barrel inner diameter for wear. Continued scraping burns the screw and scores the barrel, the most expensive failure in extrusion.
Hopper Bridging and Idling
Symptom: An irregular, intermittent change in motor tone as the screw loses material and then bites again; a hollow, unloaded whine followed by a load thump. Possible location: the feed throat and hopper, especially with awkward powders, regrind, or moist material. Frequency signature: no bearing signature, but a fluctuating 1X motor current and vibration that wanders with feed. Verification: observe feed consistency and screw fill; a stroboscopic or simply visual check of the hopper shows rat-holing or bridging. Action: improve feed with agitation, a crammer feeder, or dried material; do not let the starved screw run at high speed against empty barrel, which invites metal-to-metal contact.
Melt Pressure Pulsation Inducing Low-Frequency Jitter
Symptom: A low-frequency shudder or pulsation through the whole machine, often felt more than heard, with surging output. Possible location: the melt pump (gear pump), screen changer, or dead spots in the screw mixing section. Frequency signature: a low-frequency component, often below 10 Hz, tied to pump or screw speed; visible as pressure wave on the melt gauge. Verification: record melt pressure over time and overlay with vibration; correlated pulsation confirms the source. Action: service the melt pump, replace a clogged screen, or adjust screw speed and temperature profile to smooth the melt.
Motor Bearing Deterioration
Symptom: A rising electrical-machine whine plus a subtle cyclic click at the drive end. Possible location: the motor drive-end or non-drive-end bearing. Frequency signature: BPFI or BPFO in the envelope spectrum well before audible failure. Verification: measure motor bearing housing vibration in all three axes; compare with the baseline. Action: plan a motor bearing change on the next planned stop; motor bearings are cheap and fast to replace compared with the downtime of a seized motor.
Injection Molding and Injection Stretch Blow Diagnosis
Injection molding machines and injection stretch blow molding (ISBM) machines add hydraulic and toggle mechanisms to the rotating-element faults found in extruders, producing a distinct family of sound signatures.
Toggle Clamp Pin Wear and Noise
Symptom: A metallic knocking at the clamp end during mold closing and opening, growing as the machine cycles. Possible location: the toggle link pins and bushings, which wear from repeated high clamp force. Frequency signature: an impact at the clamp cycling rate (once or twice per cycle), visible as a spike at cycle frequency rather than shaft frequency. Verification: the listening rod at each pin joint localizes the loose one; visual check for elongation of the pin hole. Action: ream and bush the joint or replace pins; a loose toggle loses clamp force accuracy and can fracture a link.
Tie Bar Poor Lubrication
Symptom: A dry squeak or groan as the platen travels along the tie bars. Possible location: the four tie bars and their guide bushings. Frequency signature: a continuous tone modulated by platen travel speed, not a rotating frequency. Verification: listen along the tie bar guide; check lubrication lines. Action: restore automatic lubrication and clean the guide surfaces; neglected tie bars bind and distort the platen, hurting molded part quality.
Hydraulic Pump Cavitation (High-Frequency Whine)
Symptom: A sharp, high-frequency whine from the pump that changes with throttle, often compared to a tea kettle. Possible location: the main hydraulic pump, caused by low reservoir level, clogged inlet filter, or air ingestion. Frequency signature: a high-frequency broadband noise centered above 1 kHz with no clean tonal peak; the envelope spectrum shows no bearing defect, distinguishing it from a failing pump bearing. Verification: check reservoir level, suction line for air leaks, and inlet filter differential pressure. Action: refill and de-aerate the tank, replace the suction filter; prolonged cavitation erodes the pump vanes or pistons and introduces contamination.
Relief Valve Squeal
Symptom: A piercing squeal from the valve block under pressure. Possible location: a pressure relief or proportional valve with worn or contaminated spool. Frequency signature: a tonal squeal in the audible range that tracks system pressure. Verification: localize with the listening rod at the valve manifold; confirm with pressure stability data. Action: service or replace the valve, and improve oil filtration; a singing relief valve wastes energy and masks other faults.
Hydraulic Cylinder Stick-Slip Crawl
Symptom: A jerky, crawling motion of a clamp or ejector hydraulic cylinder, sometimes with a low rubbing-chatter sound. Possible location: the hydraulic cylinder rod seal, air in the line, or a sticking spool. Frequency signature: a low-frequency, irregular pulsation tied to cylinder stroke, not a rotating frequency. Verification: observe the actuator motion for stepwise movement; bleed air from the line. Action: bleed air, check rod seal, verify servo or directional valve response; stick-slip destroys positioning repeatability.
Screw Non-Return Ring Damage
Symptom: A change in injection consistency, with a soft internal knock at the screw tip during recovery. Possible location: the non-return (check) ring at the screw tip. Frequency signature: no clean tonal peak; a change in the acoustic character at the screw front during plasticizing. Verification: measure shot-to-shot weight variation and decompression; inspect the ring. Action: replace the ring and inspect the seat; a leaking ring ruins dosing accuracy and part weight.
Extrusion Blow Molding Diagnosis
Extrusion blow molding (EBM) machines add continuous extrusion, parison cutting, and a moving clamp carriage to the fault catalog, each with its own signature.
Clamp Carriage Rail Noise
Symptom: A grating or rumbling as the clamp carriage traverses or indexes. Possible location: the carriage guide rails and rollers. Frequency signature: a tone modulated by carriage travel speed, not a shaft rotation. Verification: the listening rod along the rail; inspect for brinelling or lack of grease. Action: realign and lubricate the rail, replace worn rollers; a binding carriage slows the cycle and wears the drive.
Accumulator Piston Seal
Symptom: A soft thud or sigh at the end of each shot as the accumulator strokes, with falling head pressure stability. Possible location: the accumulator piston seal allowing melt bypass. Frequency signature: a low-frequency pulse at the shot rate; pressure trace shows droop. Verification: observe parison weight variation and pressure decay after stroke. Action: rebuild the accumulator seals; a leaking piston starves the parison and ruins wall thickness.
Cutter Mechanism Impact
Symptom: A sharp periodic clang as the parison is cut. Possible location: the flying knife or hot-wire cutter mechanism and its drive. Frequency signature: a high-amplitude impact at the cut rate (once or twice per cycle). Verification: watch the cut quality and listen at the cutter; check blade sharpness and knife drive backlash. Action: sharpen or replace the blade, tighten the drive; a ragged cut drags parison weight and creates flash.
PET Bottle Blowing Machine Diagnosis
High-speed PET bottle blow molding is dominated by fast rotating and indexing mechanisms where balance and timing are everything.
High-Speed Spindle Imbalance
Symptom: A smooth but strong 1X vibration and a low roar that rises with RPM; the whole module shakes. Possible location: the blow wheel or transfer spindle. Frequency signature: a dominant 1X peak with little harmonic content; phase measurement shows a single high spot. Verification: single-plane or two-plane balancing check; compare with the baseline. Action: rebalance the wheel or replace a worn bearing hub; imbalance grows exponentially with speed and will quickly damage bearings.
Cam Mechanism Impact
Symptom: A rhythmic knocking at the cam indexing points. Possible location: the cam followers and indexing cam. Frequency signature: an impact at the cam event rate, often with 1X and 2X of the cam shaft. Verification: listen at the cam box; check follower roller wear and cam lubrication. Action: adjust cam timing, replace worn followers, restore lubrication; a damaged cam throws off bottle timing and causes jams.
Air Exhaust Noise
Symptom: A loud hiss at blow and exhaust, sometimes with a whistle if a muffler is clogged. Possible location: the high-pressure blow valves and exhaust mufflers. Frequency signature: broadband air noise, not a rotating tone; a whistle indicates a constricted path. Verification: localize at the valve block and muffler; check pressure recovery. Action: clean or replace mufflers, service valves; excess noise signals wasted compressed air and lost energy.
Recycling and Washing Line Diagnosis
Recycling and washing lines are the most abusive environment in the plant: wet, dirty, abrasive, and full of impact loads from crushers and washers.
Crusher Blade Chipping and Bearing Wear
Symptom: An irregular banging as blades strike contamination, plus a rising rumble from the rotor bearing. Possible location: the crusher rotor and its bearings. Frequency signature: random impacts at blade-pass rate with a developing BPFI envelope peak from the bearing. Verification: inspect blades for nicks, measure bearing vibration; magnetic plug shows metal. Action: rotate or resharpen blades, replace the bearing before it seizes; a seized crusher stops the whole line.
Friction Washer Particle Impact
Symptom: A continuous rattling and slapping from the friction washer. Possible location: the rotor paddles and the particle stream. Frequency signature: broadband impact noise scaling with throughput; no bearing tone unless a bearing fails. Verification: confirm the noise scales with feed and is not a bearing; inspect paddles. Action: remove oversize contamination, check paddle wear; excessive impact indicates wrong feed size.
Dewatering Rotor Imbalance
Symptom: A strong 1X shake from the dewatering centrifuge. Possible location: the dewatering machine rotor, often from material build-up on the basket. Frequency signature: dominant 1X with phase indicating imbalance. Verification: balance check; inspect for caked material. Action: clean the basket, rebalance; an unbalanced centrifuge destroys its bearings quickly.
Wash Water Pump Cavitation
Symptom: A high-frequency whine from the water pump. Possible location: the circulation pump suction. Frequency signature: high-frequency broadband, no bearing defect in envelope. Verification: check strainer and level; confirm with flow drop. Action: clear the strainer, raise level; cavitation erodes the impeller.
Pelletizing Line Diagnosis
Pelletizing lines concentrate cutting and pumping faults, where rotational balance and blade fit dominate.
Pelletizer Cutterhead Imbalance
Symptom: A 1X vibration and a throbbing hum from the cutting head. Possible location: the rotary cutterhead. Frequency signature: dominant 1X. Verification: balance check. Action: clean and rebalance the head; imbalance shortens blade and bearing life.
Die-Face Blade Fit Anomaly
Symptom: A scraping or chattering at the die face, with off-spec pellet length. Possible location: the stationary or rotating blades against the die plate. Frequency signature: a tonal scrape near cutter speed with irregular modulation. Verification: inspect blade gap and die face flatness. Action: reset the blade gap, reface the die; poor fit wastes material as fines and longs.
Water Ring Pump
Symptom: A low rumble and falling flow from the water ring system. Possible location: the circulating pump. Frequency signature: 1X with possible cavitation broadband if starved. Verification: check seal and level. Action: service the pump; a weak water ring strands hot pellets.
Fault Tree and Sound-to-Cause Lookup Table
The table below maps the most common sound characters to their frequency range, likely root cause, urgency, and the first corrective action. Use it as a quick field reference; always confirm with the machine-specific sections above before teardown.
| Sound Type | Frequency Range | Typical Root Cause | Urgency | First Action |
|---|---|---|---|---|
| Whine (high, tonal) | 1 kHz to 8 kHz | Hydraulic pump cavitation, valve squeal, worn motor bearing tone | Medium to High | Check fluid level, suction filter, valve spool; envelope-test bearing |
| Knocking (rhythmic) | At shaft or cycle rate, 2 Hz to 50 Hz | Broken gear tooth, loose toggle pin, cutter impact, cam wear | High to Critical | Stop loaded machine; FFT and ferrography; inspect gear or linkage |
| Rumble (low, continuous) | 10 Hz to 200 Hz | Thrust bearing wear, rotor imbalance, worn roller bearing | Medium to High | Measure 1X and envelope BPFI/BPFO; plan bearing change |
| Grinding (harsh, broadband) | Broadband, no clean tone | Screw-barrel scoring, dry guide, contaminated gear mesh | High to Critical | Stop; inspect contact surfaces; check lubrication and contamination |
| Periodic impact | At event rate, 1 Hz to 30 Hz | Blade chipping, loose component, clutch or cam strike | Medium to High | Localize with listening rod; tighten or replace component |
| Air hiss / whistle | Broadband and high tonal | Compressed-air exhaust, clogged muffler, leaking seal | Low to Medium | Clean muffler, service valve, check seal; recover lost energy |
Vibration Severity Standards (ISO 10816 / ISO 20816)
ISO 10816 and the consolidated ISO 20816 family classify machines by power and mounting, then set zone boundaries for overall vibration velocity in mm/s RMS measured on the bearing housing. The representative values below follow the standard’s evaluation zones for typical plastic machinery classes. Always confirm the exact class and foundation type for your machine, and treat these as guidance rather than a substitute for the published standard.
| Machine Class | Power / Type | Zone A (Good) | Zone B (Satisfactory) | Zone C (Unsatisfactory) | Zone D (Unacceptable) |
|---|---|---|---|---|---|
| Class I | Small, under 15 kW | up to 0.71 | 0.71 to 1.8 | 1.8 to 4.5 | above 4.5 |
| Class II | Medium, 15 to 300 kW | up to 1.12 | 1.12 to 2.8 | 2.8 to 7.1 | above 7.1 |
| Class III | Large, 300 kW to 50 MW | up to 1.8 | 1.8 to 4.5 | 4.5 to 11.2 | above 11.2 |
| Class IV | Large turbo, over 50 MW | up to 2.8 | 2.8 to 7.1 | 7.1 to 18 | above 18 |
Measure in millimeters per second RMS at the bearing housing, in three directions, at operating speed and load. A machine newly commissioned by Wanplas typically sits in Zone A or low Zone B; a reading that climbs into Zone C during a trend is your signal to schedule intervention, and any excursion into Zone D means stop and repair. Note that flexible-mounted machines and those on isolation pads are evaluated with slightly relaxed limits, so record the mounting type in your baseline.
Spectral Identification of Six Typical Faults
The following table is the spectrum analyst’s quick key. It lists the six dominant fault families, their characteristic frequency content, and the supporting clues that separate them from look-alikes.
| Fault Family | Dominant Frequency | Waveform / Phase Clue | Supporting Evidence |
|---|---|---|---|
| Unbalance | 1X (rarely 2X) | Single high spot, stable phase, pure sinusoid | Vibration largest in radial direction, grows with speed squared |
| Misalignment | 1X and strong 2X, sometimes 3X | Axial vibration high, phase differs across coupling | Often with elevated temperature at coupling; angular type shows 2X |
| Looseness (mechanical) | 1X plus harmonics, subharmonics | Distorted, clipped waveform; rattling | Vibration changes with direction; noticeable at structural joints |
| Bearing defect | BPFO / BPFI / BSF / FTF with 1X sidebands | Impacts in envelope, not time domain | Clear only after envelope demodulation; rising temperature |
| Gear fault | GMF with sidebands at gear shaft 1X | Amplitude modulation at shaft speed | Ferrography shows fatigue particles; local gear mesh tone |
| Cavitation | High-frequency broadband above 1 kHz | No tonal peak, random; no bearing defect in envelope | Linked to suction conditions; flow and pressure instability |
Inspection Routines and Predictive Maintenance
A diagnosis method is only as good as the routine that sustains it. The table below defines a practical inspection cadence that scales from a single shift pen-check to a full predictive maintenance (PdM) program. Investment levels are given as Low, Medium, High, or Very High to respect the no-currency rule; the only stated amount is the Wanplas shared free-parts allowance of USD 500 per year.
| Interval | Action | Instrument | Record | Investment Level |
|---|---|---|---|---|
| Daily | Listen for new tones; feel bearing temp by hand; check oil sight glass | Listening rod, hand | Log anomalies in shift book | Low |
| Weekly | Vibration pen reading at fixed points; magnetic plug check on key gearboxes | Vibration pen, magnet plug | Trend spreadsheet per machine | Low |
| Monthly | FFT spot check on critical machines; infrared scan of motors and gearboxes | FFT analyzer, IR camera | Spectrum archive, thermal log | Medium |
| Quarterly | Oil sample and ferrography on large drives; full route with envelope on bearings | Ferrography kit, envelope analyzer | Wear particle report, PdM review | Medium to High |
The predictive maintenance landing path moves through three stages. Stage one, Low investment, is the route-and-baseline discipline above; it catches gross faults and builds the data history. Stage two, Medium investment, adds a portable FFT and envelope analyzer plus training so your engineers can classify faults by spectrum. Stage three, High or Very High investment, installs permanent online sensors on the most critical machines with automatic alarm at zone crossings and remote expert review. Choose the stage by downtime cost sensitivity: a line that loses a large amount per hour of stoppage justifies Very High investment, while a backup line may stay at Low.
Wanplas Group Machinery and Diagnosis Specification Tables
Wanplas is the main brand covering the full plastic machinery value chain, and it builds through specialized factories, each a leader in one category. Because this is the group main site, the diagnostic points below name the relevant Wanplas factory and its machines, so a plant can match the fault method to the exact equipment it runs.
Kerke Twin-Screw Extruders (Compounding)
Kerke, a Wanplas factory, builds co-rotating parallel twin-screw compounding extruders from the KTE-16B laboratory unit up to the KTE-135D production machine. These high-torque, high-speed gearboxes are the most diagnosis-sensitive part of any compounding line, and the table below gives the reference points an engineer should baseline at commissioning.
| Parameter | KTE-65B Reference | KTE-95B Reference | KTE-135D Reference | Diagnosis Note |
|---|---|---|---|---|
| Screw diameter (mm) | 65 | 95 | 135 | Larger units need lower baseline velocity limits |
| L/D ratio | 40 to 52 | 40 to 52 | 40 to 52 | Longer L/D raises thrust load; watch thrust bearing |
| Drive power (kW) | about 132 | about 315 | about 710 | Class II to Class III on ISO 10816 |
| Max screw speed (rpm) | about 600 | about 500 | about 400 | 1X at full speed: 10 / 8.3 / 6.7 Hz |
| Baseline gearbox velocity (mm/s) | under 2.0 | under 2.5 | under 3.0 | Target Zone A or low Zone B |
| Thrust bearing check | Envelope monthly | Envelope monthly | Envelope weekly | Largest machines get the tightest schedule |
Apollo Extrusion Blow Molding Machines
Apollo, a Wanplas factory with over 20 years in extrusion blow molding, builds the ABLB series (200 mL to 20 L), the ABLD heavy-duty series (20 L to 1500 L), and a fully electric series. The moving clamp carriage and accumulator are the distinctive diagnosis points; baseline the carriage rail noise and the accumulator piston stroke as described in Section 5.
| Parameter | ABLB 55 | ABLD 150 | Fully Electric 10L | Diagnosis Note |
|---|---|---|---|---|
| Container range | 2 L to 3 L | up to 150 L | 200 mL to 20 L | Larger vessels amplify carriage rail faults |
| Clamp type | Hydraulic toggle | Hydraulic toggle | Electric servo | Listen for toggle pin knock; electric is quieter |
| Accumulator | Optional | Standard | Direct extrusion | Check piston seal thud on ABLD |
| Rail inspection | Weekly | Weekly | Monthly | Grease and align to kill rumble |
| Typical noise floor (dB(A)) | 78 to 85 | 80 to 88 | 72 to 80 | Electric series lowers airborne noise |
YuDa PET Bottle Blow Molding Machines
YuDa, a Wanplas factory and a top PET bottle blow machine builder with more than 20 years and 20-plus patents, runs the FGX high-speed series up to 15000 BPH. At those speeds, spindle imbalance and cam timing are the dominant faults; the 38.1 mm heater pitch and remote monitoring help but do not remove the need for balance checks.
Aibim Injection Stretch Blow Molding Machines
Aibim, a Wanplas factory, builds the three-station one-step IBM series (IBM55 hybrid, IBM65, IBM75) covering 3 mL to 1000 mL. Its PREFILL hydraulic technology saves at least 35 percent energy, and the CE-certified stripper station improves safety, but the rotating transfer and cam still need periodic impact listening as in Section 6.
Polyretec Recycling and Washing Lines
Polyretec, a Wanplas factory with roots back to 2010, builds washing lines from 500 kg/h to 6000 kg/h and new-generation pelletizing lines. The crusher, friction washer, and dewatering machine are the impact and imbalance centers; follow Section 7 and keep the magnetic plug clean.
Faygo Pipe and Profile Extrusion Lines
Faygo, a Wanplas factory with 22 years in pipe and profile extrusion, builds PVC, PE, PP-R, and corrugated lines and runs 72-hour continuous testing before delivery. The extruder gearbox and vacuum sizing follow the extruder diagnosis of Section 3, while corrugator chains add a rhythmic click to watch.
YuanSu Film, Sheet, and Board Extrusion Lines
YuanSu, a Wanplas factory, builds film (0.008 mm to 0.25 mm), sheet (0.25 mm to 2 mm), and board (3 mm to 50 mm) lines. The high-torque gearbox and chill-roll drive are the vibration-sensitive points; baseline the roll drive bearings and watch for the low-frequency pulsation of melt pressure instability from Section 3.
Application Industries
The diagnosis method above serves every industry that runs Wanplas group machines. The compounding extruders from Kerke feed masterbatch and engineering plastic producers in packaging, automotive, and cable. The blow molding and bottle blowing machines from Apollo, Aibim, and YuDa supply food and beverage, daily chemical, medical and pharmaceutical, and cosmetic containers. The recycling and washing lines from Polyretec serve sustainability-driven plants turning post-consumer waste into reusable pellets. The pipe and profile lines from Faygo serve construction, municipal water and gas, agricultural irrigation, and cable protection. The film, sheet, and board lines from YuanSu serve packaging, construction and waterproofing, automotive and appliance, lithium battery and photovoltaic, and medical protection. A single plant often runs machines from several Wanplas factories, and the unified sound-and-vibration method means one trained team can cover all of them.
Requirement-to-Solution Recommendation
The table below helps a plant manager choose a diagnosis program and instrument configuration based on scale, equipment type, and how sensitive they are to downtime cost. Investment levels are expressed as Low, Medium, High, or Very High.
| Factory Scale | Equipment Type | Downtime Cost Sensitivity | Recommended Inspection Plan | Equipment Configuration |
|---|---|---|---|---|
| Small shop, 1 to 3 machines | Single extruder or blow molder | Low | Daily listen, weekly pen | Listening rod, vibration pen, IR thermometer (Low) |
| Medium plant, 4 to 15 machines | Mixed extrusion and molding | Medium | Weekly pen, monthly FFT on critical | Plus portable FFT and envelope analyzer (Medium) |
| Large plant, 16 to 50 machines | Full compounding to recycling | High | Route plus quarterly ferrography | FFT, envelope, ferrography, IR (Medium to High) |
| Continuous 24/7 operation | Critical single line, no backup | Very High | Online monitoring with auto-alarm | Permanent sensors, remote expert review (Very High) |
| Multi-site group | All categories across sites | High to Very High | Centralized PdM with shared baseline | Online plus portable kits per site (Very High) |
Wanplas Service and Support
Wanplas and its factories back every machine with a shared service promise that makes the diagnosis method practical to operate. Remote diagnosis support lets an engineer at the Wanplas technical center read PLC and analyzer data from a client site to confirm a bearing or gear fault without a flight. Spare parts supply keeps critical bearings, seals, blades, and gears in stock so a planned change-out stays planned; the group policy includes USD 500 of free parts every year per machine under the standard agreement, with free replacement of damaged parts inside the warranty window. Engineer on-site service handles installation, commissioning, and teardown when a fault is confirmed. A structured training system teaches your maintenance staff to run the listening route, read the vibration pen, and interpret FFT and envelope spectra, so the program survives staff turnover. Finally, the open-factory policy welcomes customers to visit the plants, watch machines run, and practice diagnosis on live equipment before taking the method home.
Frequently Asked Questions
What is the difference between dB(A) sound measurement and mm/s vibration measurement?
Sound pressure in dB(A) captures airborne pressure waves and is best for air-path faults like cavitation, valve squeal, and exhaust noise. Vibration velocity in mm/s RMS captures structural motion through the machine frame and is best for internal faults like imbalance, misalignment, and bearing defects. A complete program uses both, because some faults are loud but low-vibration and others are violent but quiet.
How early can envelope demodulation detect a failing bearing?
Envelope demodulation typically reveals a bearing defect months before the fault becomes audible or before the overall velocity leaves Zone B. The defect frequency appears in the envelope spectrum while the time-domain trace and the overall level still look normal, which is exactly why it is the cornerstone of predictive maintenance.
Can I rely on a smartphone vibration app for severity decisions?
No. A smartphone app uses an uncalibrated consumer accelerometer with low sampling rate and no real FFT or envelope analysis, so it cannot classify severity or identify bearing frequencies. Use it only to confirm that a machine is shaking, then confirm with a calibrated vibration pen or analyzer before any maintenance decision.
Why does my extruder rumble more when melt pressure is high?
A rising low-frequency rumble that scales with head pressure points to thrust bearing wear, because the thrust bearing absorbs the axial force from melt pressure pushing back on the screw. Verify with the listening rod at the thrust housing and an envelope check of the thrust bearing; plan a change-out before axial play damages the screw and barrel.
What vibration velocity limit should I treat as a stop signal?
Follow the ISO 10816 / ISO 20816 zone boundaries by machine class: for a medium 15 to 300 kW machine, any reading above 7.1 mm/s RMS (Zone D) means stop and repair. More useful than a single limit is the trend — a steady climb into Zone C during your route is the signal to schedule intervention before you reach Zone D.
How often should I take oil samples for ferrography?
For critical high-power gearboxes, sample quarterly as part of a predictive program; for smaller or backup machines, semiannual is enough. Combine ferrography with the magnetic plug check every week, because a plug heavy with fine metal often precedes the formal sample result and lets you act earlier.
Which Wanplas factory builds the machine I should baseline first?
Baseline the machine whose stoppage costs you the most. If that is a compounding line, start with Kerke twin-screw extruders; if it is container production, start with Apollo, Aibim, or YuDa blow molding machines; if it is sustainability output, start with Polyretec recycling lines; if it is pipe or sheet, start with Faygo or YuanSu. The unified method means one trained team covers all of them.
Is a high-pitched whine always a bearing fault?
No. A high-frequency whine is just as often hydraulic pump cavitation or a relief valve squeal, both of which show broadband high-frequency noise with no bearing defect in the envelope spectrum. Confirm by checking fluid level, suction filter, and valve spool before assuming a bearing change is needed.
When your team is ready to put this method into practice, send Wanplas your machine list, operating speeds, and the faults you see most often, and the group will help configure a diagnosis route, recommend the right instrument tier for your downtime sensitivity, and arrange engineer training or a factory visit so your staff can learn the listening and spectrum skills on live equipment. Wanplas and its specialized factories stand behind every machine with remote diagnosis support, spare parts supply including USD 500 of free parts per year under the standard agreement, on-site service, and an open-factory policy that welcomes you to verify quality and method in person.
